At early stages of development, neuronal cultures in vitro
spontaneously reach a coherent state of collective firing in a pattern
of nearly periodic global bursts. Although understanding the
spontaneous activity of neuronal networks is of chief importance in
neuroscience, the origin and nature of that pulsation has remained
elusive. By combining high-resolution calcium imaging with modelling
in silico, we show that this behaviour is controlled by the
propagation of waves that nucleate randomly in a set of points that is
specific to each culture and is selected by a non-trivial interplay
between dynamics and topology. The phenomenon is explained by the
noise focusing effect--a strong spatio-temporal localization of the
noise dynamics that originates in the complex structure of avalanches
of spontaneous activity. A detailed explanation of the phenomenon is
provided together with an accurate characterization of avalanches with
power-law statistics. The emergence of a complex hierarchical
functional network with effective scale-free structure out of the
underlying Gaussian network with metric correlations, due to the
integrate-and-fire dynamics, is discussed. A coarse-grained continuum
model is introduced to describe neuronal tissues in terms of an
effective excitable medium subject to unusual noise dynamics.
Implications of our results in other complex systems, such as in the
propagation of rumors in social networks are discussed.
References:
J.G.Orlandi et al., Nature Physics 9, 582-590 (2013). DOI:
10.1038/nphys2686J.M. Beggs Nature Physics 9, 533-534 (2013) DOI:
10.1038/nphys2707